Radiation curable etch resistant inkjet ink printing

ABSTRACT

An inkjet printing radiation curable inkjet ink for forming a protective layer during an etching process includes at least 70 percent by weight of a polymerizable composition based on the total weight of radiation curable inkjet ink, wherein the polymerizable composition has an oxygen fraction OFR&gt;0.250 and a weighted polymerizable functionality WPF≧0.0050, and the polymerizable composition contains no polymerizable compound with an ethylenic double bond and including a phosphoester group or a carboxylic acid group in the molecule thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2013/050943, filed Jan. 18, 2013. This application claims thebenefit of U.S. Provisional Application No. 61/593,338, filed Feb. 1,2012, which is incorporated by reference herein in its entirety. Inaddition, this application claims the benefit of European ApplicationNo. 12153196.6, filed Jan. 31, 2012, which is also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to inkjet printing of radiation curableinkjet inks that are etch resistant.

2. Description of the Related Art

Etching is the process of using a chemical, usually a strong acid ormordant, to cut into the unprotected parts of a metal surface in orderto create a conductive pattern, e.g. a printed circuit board, or adesign for decorative purposes.

Printed circuit boards are generally made by bonding a layer of copperover the entire substrate, applying a temporary mask and removing byetching unwanted copper leaving only the desired conductive copperpattern.

The temporary mask can be made by screen printing etch resistant inkonto the copper foil. The screen printing method by nature has lowresolution and requires a relatively high viscosity for avoiding adversephenomena such as bleeding and smudges.

Another method to provide a temporary mask is photoengraving. Aphotomask is usually prepared by laser-printing an image onto atransparent film using computer-aided manufacturing software. Afterexposing the photoresist coating on the copper foil through thephotomask, a developer removes the non-exposed photoresist coating.Although high-resolution conductive patterns can be made, this methodresults in extra cost and chemical waste. Direct laser imagingtechniques were developed which reduced the chemical waste.

U.S. Pat. No. 5,270,368 (VIDEOJET) discloses a UV curable,etch-resistant ink for inkjet printing circuit boards comprising a resinformulation having at least two acrylate components, one of which is anaromatic acrylate having a pendant carboxyl group and one of which is anacrylated epoxy monomer or dimer, a photoinitiator and an organiccarrier. The preferred organic carrier of methanol and methyl ethylketone is employed in a range of 40% to 90% by weight of the inkcomposition. These volatile organic solvents lead to latency problems ofinkjet print heads making reliable inkjet printing in an industrialenvironment process problematic. Reducing the amount of organic solventleads to a too high ink viscosity, because some aromatic acrylatecompounds traditionally used for preparing photoresist coatings havevery high viscosity. For example, the bisphenol A ethoxylated diacrylate(Photomer™ 4028) used in all the examples of U.S. Pat. No. 5,270,368(VIDEOJET) has a viscosity of 800 to 1200 mPa·s at 25° C. These aromaticacrylate compounds are essential for having a good balance in adhesionso that the printed ink layer is etch resistant yet easily removableafter etching, especially since many different etching conditions andetchants are used in industry.

In another approach, polymerizable acidic compounds are included in theradiation curable ink to promote adhesion to the metal surface. Forexample US 2011024392 A (NISSHIN STEEL & TOKYO PRINTING INK MFG CO)discloses an etch resist inkjet ink having excellent adhesion tometallic plates by including a specific polymerizable phosphoric estercompound, a polyfunctional monomer having two or more ethylenicdouble-bond groups per molecule and having no phosphoric ester group anda monofunctional monomer having one ethylenic double-bond group permolecule and having neither phosphoric ester group nor carboxy group.

WO 2004106437 A1 (AVECIA) discloses a process for etching a metal oralloy surface which comprises applying an etchresistant ink by ink jetprinting to selected areas of the metal or alloy, exposing theetch-resistant ink to actinic radiation and/or particle beam radiationto effect polymerisation, optionally thermally treating theetch-resistant ink and then removing the exposed metal or alloy by achemical etching process wherein the etch-resistant ink is substantiallysolvent-free. All the disclosed etch-resistant inks include an acidicpolymerizable compound.

WO 2004462260 A2 (MARKEM) discloses a radiation-curable hot melt inkcomposition comprising: a colorant; a polymerizable monomer; and aphotoinitiating system comprising 0.5-1.5% by weight of an aromaticketone photoinitiator, 2-10% by weight of an amine synergist, 3-8% byweight of an alpha-cleavage type photoinitiator, and 0.5-1.5% by weightof a photosensitizer.

However, the inclusion of acidic polymerizable compounds has someundesirable side effects such as increased viscosity and decreased inkstability and curing speed.

Hence, there remains a need for improved low viscous radiation curableinkjet inks suitable for reliable inkjet printing in an (industrial)etching process and applicable to a wide range of etchants and etchingconditions.

SUMMARY OF THE INVENTION

It was surprisingly found that the above cited problems could be solvedby radiation curable inkjet inks including at least 70 percent by weightof a polymerizable composition based on the total weight of radiationcurable inkjet ink, wherein the polymerizable composition was controlledto have a minimum oxygen content and cross linking capability, andwithout the need of an acidic monomer for improving adhesion to themetal surface.

Preferred embodiments of the invention have been realised with a methodof inkjet printing as defined below.

Further preferred embodiments of the invention will become apparent fromthe description hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Definitions

The term “radiation curable ink” means that the ink is curable by UVradiation or by e-beam.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. methyl, ethyl, for three carbon atoms:n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl andtertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl,2,2-dimethylpropyl and 2-methyl-butyl etc.

The term “monofunctional monomer” means a monomer having only onepolymerizable group, for example an acrylate group.

The term “polyfunctional monomer” means a monomer having two, three ormore polymerizable groups, e.g. two acrylate groups and one vinyl ethergroup.

The term “polyacrylate” means a monomer having two, three or moreacrylate groups.

Methods of Inkjet Printing

A method of inkjet printing according to a preferred embodiment of thepresent invention includes the steps of:

-   a) forming a protected area on a metal surface by printing and    curing a radiation curable inkjet ink on the metal surface;-   b) removing metal from the unprotected area of the metal surface by    etching; and-   c) removing at least partially the cured radiation curable inkjet    ink from the protected area of the metal surface; characterized in    that the radiation curable inkjet ink includes at least 70 percent    by weight of a polymerizable composition based on the total weight    of radiation curable inkjet ink, wherein the polymerizable    composition has an oxygen fraction OFR>0.250 and a weighted    polymerizable functionality WPF 0.0050, wherein

${OFR} = {{\sum\limits_{i = 1}^{n}{\frac{15.9994 \times N_{O,i} \times \% \mspace{14mu} {wt}_{i}}{{MW}_{i} \times \% \mspace{14mu} {wt}_{P}}\mspace{14mu} {and}\mspace{14mu} {WPF}}} = {\sum\limits_{i = 1}^{n}\frac{N_{P,i} \times \% \mspace{14mu} {wt}_{i}}{{MW}_{i} \times \% \mspace{14mu} {wt}_{P}}}}$

with:

-   n=the number of polymerizable compounds in the polymerizable    composition having a different chemical structural formula;-   N_(O,i)=the number of oxygen atoms in polymerizable compound i;-   N_(P,i)=the number of polymerizable groups in polymerizable compound    i;-   MW_(i)=the molecular weight of the polymerizable compound i;-   % wt_(i)=the weight percentage of the polymerizable compound i based    on the total weight of the radiation curable inkjet ink; and-   % wt_(P)=the weight percentage of the polymerizable composition    based on the total weight of the radiation curable inkjet ink, and-   wherein the polymerizable composition contains no polymerizable    compound with an ethylenic double bond and including a phosphoester    group or a carboxylic acid group in the molecule thereof.

The manner to calculate the oxygen fraction OFR and the weightedpolymerizable functionality WPF is exemplified here below. If aradiation curable inkjet ink contains a single polymerizable compound inthe polymerizable composition of radiation curable inkjet ink, then thevalue of i and n are both 1.

Assumed that the radiation curable inkjet ink contains % wt_(P)=80 wt %of a polymerizable composition consisting of two (n=2) monomers A and Bpresent in an amount of % wt₁=30 wt % respectively % wt₂=50 wt % allbased on the total weight of the radiation curable inkjet ink.

Monomer A is 2-(2′-vinyloxyethoxy)ethylacrylate having a molecularweight MW₁ of 186.21 and containing 4 oxygen atoms (N_(O,1)=4) and 2polymerizable groups, i.e. an acrylate group and a vinylether group, sothat N_(P,1)=2.

Monomer B is dipropylene glycol diacrylate having a molecular weight MW₁of 242.27 and contains 5 oxygen atoms (N_(O,2)=5) and 2 polymerizablegroups, i.e. two acrylate groups, so that N_(P,2)=2.

This results in:

OFR=[(15.9994×4×30)/(186.21×80)]+[(15.9994×5×50)/(242.27×80)]=0.129+0.206=0.335and

WPF=[(2×30)/(186.21×80)]+[(2×50)/(242.27×80)]=0.0040+0.0052=0.0092

Metal Surfaces

There is no limitation on the nature of the metal surface. The metalsurfaces preferably consist of copper, aluminium, nickel, iron, tin,titanium or zinc, but may be also be alloys including these metals. In avery preferred embodiment, the metal surface is made of copper. Copperhas a high electrical conductivity and is a relatively cheap metal,making it very suitable for making printed circuit boards.

The metal surface may be self-supporting or may be present on a support.The support can be a non-flexible support as conventionally used in theproduction of PCB's, but may also be a flexible substrates made of e.g.polyethylene terephthalate or polyimide.

Self supporting metal surfaces are generally used when a decorativemetal panel is made. Such a decorative metal panel may serve a purposeother than being purely decorative, such as providing information. Forexample, an aluminium name plate wherein the etch resistant radiationcurable inkjet ink was printed as information, such as a name of aperson or a company, and then removed to result in a glossy shiny nameon a mat etched background, is also considered a decorative metal panelincluding a decorative element.

In another embodiment of a decorative metal panel, the metal surface isnot self-supporting and when removed by etching exposes the color of orthe information on the support.

In a preferred embodiment of the inkjet printing method, the metalsurface is cleaned before printing the radiation curable inkjet ink.This is especially desirable when the metal surface is handled by handand no gloves are worn. The cleaning removes dust particles and greasewhich can interfere in the adhesion of the radiation curable inkjet inkto the metal surface.

Etching

Etching of a metal surface, as in step b) of the inkjet printing method,is performed by using an etchant. The etchant is preferably an aqueoussolution having a pH<3 or wherein 8<pH<10.

In a preferred embodiment, the etchant is an acid aqueous solutionhaving a pH of less than 2. The acid etchant preferably includes atleast one acid selected from the group consisting of nitric acid, picricacid, hydrochloric acid, hydrofluoric acid and sulfuric acid.

Preferred etchants known in the art include Kalling's N° 2, AS™ N° 30,Kellers Etch, Klemm's Reagent, Kroll's Reagent, Marble's Reagent,Murakami's Reagent, Picral and Vilella's Reagent.

In another preferred embodiment, the etchant is an alkaline aqueoussolution having a pH of no more than 9. The alkaline etchant preferablyincludes at least one base selected from the group consisting of ammoniaor ammonium hydroxide, potassium hydroxide and sodium hydroxide.

The etchant may also contain a metal salt such as copper dichloride,copper sulphate, potassium ferricyanide and iron trichloride.

Etching is preferably performed in a time frame of seconds to a fewminutes, more preferably 5 to 100 seconds. Etching is preferablyperformed at room temperature (20° C.)

Etching is preferably followed by rinsing with water to remove anyresidual etchant.

Stripping

After etching, the cured radiation curable inkjet ink must at leastpartially be removed from the metal surface, so that e.g. electric orelectronic devices can make contact with the remaining metal surface(conductive pattern) or that the decorative feature of an etched metalpanel becomes fully visible. For example, an electronic component suchas a transistor must be able to make electrical contacts with theconductive (copper) pattern on the printed circuit board. In a preferredembodiment, the cured radiation curable inkjet ink is completely removedfrom the metal surface.

In a preferred embodiment, the cured radiation curable inkjet ink isremoved from the protected area in step c) by an alkaline strippingbath. Such an alkaline stripping bath is usually an aqueous solutionwith a pH>10.

In a more preferred embodiment, the cured radiation curable inkjet inkis removed from the protected area in step c) by dry delamination. Thistechnique of “dry stripping” is currently unknown in the art ofmanufacturing printed circuit boards and introduces several ecologicaland economical advantages in the manufacturing process. Dry strippingnot only eliminates the need of a corrosive alkaline stripping bath andits inherent liquid waste, but also allows for a higher throughput. Drystripping can be implemented, for example, by using an adhesive foil anda roll-to-roll laminator-delaminator. The adhesive foil is firstlaminated with its adhesive side onto the cured radiation curable inkjetink present on the metal surface and subsequently delaminated therebyremoving the cured radiation curable inkjet ink from the metal surface.Delamination by a roll-to-roll laminator-delaminator can be performed inseconds, while alkaline stripping takes minutes.

INDUSTRIAL APPLICABILITY

In one preferred embodiment, the inkjet printing method of the presentinvention is used in a method for manufacturing a conductive pattern,such as a PCB. The conductive pattern corresponds to the cured radiationcurable inkjet ink having an oxygen fraction OFR>0.250 and a weightedpolymerizable functionality WPF≧0.0050.

It was found that inks including a polymerizable composition having anoxygen fraction OFR≦0.250 and a weighted polymerizable functionalityWPF≦0.0055, exhibited good etch resistance but no strippability.Although these inks are useless as etch resistant ink for creating aconductive pattern of a printed circuit board, they can be used as aso-callled “legend ink”. The legend, or nomenclature as it is alsoknown, is in the form of letters and numbers which aid the assembly andidentification of component positions. The device part number,orientation or pin one locator is usually printed with a white or yellowlegend ink. By printing the legend inkjet ink and the etch resistantinkjet ink simultaneously on a copper plate, with the legend inkjet inkbeing printed in a position not covering the conductive pattern orcopper circuitry, a simpler and cost-effective manufacturing process ofprinted circuit boards can be realized.

A solder mask is a polymeric layer providing a permanent protectivecoating for the copper traces of a printed circuit board (PCB) andprevents solder from bridging between conductors, thereby preventingshort circuits. Solder mask is traditionally green but is now availablein many colors. In the preferred embodiment where also a legend inkjetink including a polymerizable composition having an oxygen fractionOFR≦0.250 and a weighted polymerizable functionality WPF≦0.0055 isinkjet printed on the metal surface, the solder mask is preferablytranslucent or transparent, most preferably transparent. The advantageof using a transparent solder mask is that the letters and numbers ofthe legend are clearly readable and that the legend is also protectedagainst scratching. The solder mask is preferably an epoxy liquid thatis silk-screened onto the PCB.

In another preferred embodiment, the inkjet printing method of thepresent invention is used in a method for manufacturing a decorativeetched metal panel. In this case, usually not all the metal is removedfrom the metal surface. The metal panel may consist of metal or can besome kind of support with a metallic surface. In the latter, all metalcan be removed to reveal the color and texture of the support. Etchingcauses a change in optical properties of a metal surface, such as achange of gloss. After removal of the cured radiation curable inkjet inkfrom the metal surface an aesthetic effect is created between the etchedand the non-etched metal surface. In addition to the aesthetic effect byetching, one or more differently colored radiation curable inkjet inksincluding a polymerizable composition having an oxygen fractionOFR≦0.250 and a weighted polymerizable functionality WPF≦0.0055 can beprinted on the metal surface to produce permanent colored decorationalfeatures.

Radiation Curable Inkjet Inks

In a preferred embodiment of the present invention, a metal surface iscombined with a radiation curable inkjet ink including at least 70percent by weight of a polymerizable composition based on the totalweight of radiation curable inkjet ink,

wherein the polymerizable composition has an oxygen fraction OFR>0.250and a weighted polymerizable functionality WPF≧0.0050, wherein

${OFR} = {{\sum\limits_{i = 1}^{n}{\frac{15.9994 \times N_{O,i} \times \% \mspace{14mu} {wt}_{i}}{{MW}_{i} \times \% \mspace{14mu} {wt}_{P}}\mspace{14mu} {and}\mspace{14mu} {WPF}}} = {\sum\limits_{i = 1}^{n}\frac{N_{P,i} \times \% \mspace{14mu} {wt}_{i}}{{MW}_{i} \times \% \mspace{14mu} {wt}_{P}}}}$

with:

-   n=the number of polymerizable compounds in the polymerizable    composition having a different chemical structural formula;-   N_(O,i)=the number of oxygen atoms in polymerizable compound i;-   N_(P,i)=the number of polymerizable groups in the polymerizable    compound i;-   MW_(i)=the molecular weight of the polymerizable compound i;-   % wt_(i)=the weight percentage of the polymerizable compound i based    on the total weight of the radiation curable inkjet ink; and-   % wt_(P)=the weight percentage of the polymerizable composition    based on the total weight of the radiation curable inkjet ink, and    wherein the polymerizable composition contains no polymerizable    compound with an ethylenic double bond and including a phosphoester    group or a carboxylic acid group in the molecule thereof.

The combination of the metal surface and the radiation curable inkjetaccording to a preferred embodiment of the present invention may befurther combined with a radiation curable inkjet legend ink wherein thepolymerizable composition has an oxygen fraction OFR≦0.250 and aweighted polymerizable functionality WPF≦0.0055.

The radiation curable inkjet inks may be cationically curable inkjetinks but are preferably free radical curable inkjet inks. The radiationcurable inkjet inks can be cured by e-beam, but are preferably cured bylight, more preferably UV light.

In a preferred embodiment the radiation curable inkjet ink is a UVcurable inkjet ink, more preferably a free radical UV curable inkjetink.

The radiation curable ink may contain a colorant. The advantage is thatthe printed ink pattern is clearly visible which allows orienting themetal surface during handling. The colorant may be a dye or a pigment.If the colorant is a pigment preferably a dispersant is present, morepreferably a polymeric dispersant. The pigmented curable ink may containa dispersion synergist to improve the dispersion quality and stabilityof the ink.

The viscosity of the radiation curable inkjet inks is preferably smallerthan 20 mPa·s at 45° C. and at a shear rate of 1,000 s⁻¹, morepreferably between 1 and 14 mPa·s at 45° C. and a shear rate of 1,000s¹.

For high speed, high resolution printing, the viscosity measured at 45°C. is preferably smaller than 20 mPa·s, more preferably between 1 and 14mPa·s at 45° C. and at a shear rate of 90 s⁻¹. Such measurement can beperformed using a Brookfield DV-II+ viscometer at 45° C. and at 12rotations per minute.

The surface tension of the curable inkjet inks is preferably in therange of about 20 mN/m to about 70 mN/m at 25° C., more preferably inthe range of about 22 mN/m to about 40 mN/m at 25° C.

The curable inkjet inks may further also contain at least one inhibitorfor improving the thermal stability of the ink.

The curable inkjet inks may further also contain at least one surfactantfor obtaining desired spreading characteristics on a substrate.

In a preferred embodiment, the n polymerizable compounds in thecombination according to present invention all have a viscosity of lessthan 40 mPa·s at 25° C.

Polymerizable Compounds

Any monomer or oligomer, preferably capable of free radicalpolymerization, may be used as polymerizable compound. A combination ofmonomers, oligomers and/or prepolymers may also be used. The monomers,oligomers and/or prepolymers may possess different degrees offunctionality, and a mixture including combinations of mono-, di-,tri-and higher functionality monomers, oligomers and/or prepolymers maybe used. The viscosity of the radiation curable inkjet inks can beadjusted by varying the ratio between the monomers and oligomers.

Preferred monomers and oligomers are those listed in [0059] to [0115] inEP 1911814 A (AGFA GRAPHICS) incorporated herein as a specificreference.

Particularly preferred polymerizable compounds are selected from thegroup consisting of 1,6-hexanediol diacrylate, 1,4-butanedioldiacrylate, 2-(2′-vinylethoxy)ethyl acrylate, triethyleneglycoldiacrylate, triethyleneglycol dimethacrylate, propoxylatedneopentylglycol diacrylate, propoxylated glycerine triacrylate,trimethylolpropane trimethylacrylate, tripropylene glycol diacrylate,diethylene glycol diacrylate, dipropylene glycol diacrylate, ethoxylatedtrimethylolpropane triacrylate and propoxylated trimethylolpropanetriacrylate.

Photoinitiators

The photoinitiator is preferably a free radical initiator. A freeradical photoinitiator is a chemical compound that initiatespolymerization of monomers and oligomers when exposed to actinicradiation by the formation of a free radical.

Two types of free radical photoinitiators can be distinguished and usedin the inkjet inks of preferred embodiments of the present invention. ANorrish Type I initiator is an initiator which cleaves after excitation,yielding the initiating radical immediately. A Norrish type II-initiatoris a photoinitiator which is activated by actinic radiation and formsfree radicals by hydrogen abstraction from a second compound thatbecomes the actual initiating free radical. This second compound iscalled a polymerization synergist or co-initiator. Both type I and typeII photoinitiators can be used in preferred embodiments of the presentinvention, alone or in combination.

Suitable photo-initiators are disclosed in CRIVELLO, J. V., et al.VOLUME III: Photoinitiators for Free Radical Cationic. 2nd edition.Edited by BRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998.p.287-294.

Specific examples of photo-initiators may include, but are not limitedto, the following compounds or combinations thereof: benzophenone andsubstituted benzophenones, 1-hydroxycyclohexyl phenyl ketone,thioxanthones such as isopropylthioxanthone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one, benzildimethylketal, bis (2,6- dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide,2,4,6-trimethylbenzoyldiphenylphosphine oxide,2-methyl-1-[4-(methylthio) phenyl]-2-morpholinopropan-1-one,2,2-dimethoxy-1, 2-diphenylethan-1-one or 5,7-diiodo-3-butoxy-6-fluorone.

Suitable commercial photo-initiators include Irgacure™ 184, Irgacure™500, Irgacure™ 907, Irgacure™ 369, Irgacure™ 1700, Irgacure™ 651,Irgacure™ 819, Irgacure™ 1000, Irgacure™ 1300, Irgacure™ 1870, Darocur™1173, Darocur™ 2959, Darocur™ 4265 and Darocur™ ITX available from CIBASPECIALTY CHEMICALS, Lucerin™ TPO available from BASF AG, Esacure™KT046, Esacure™ KIP150, Esacure™ KT37 and Esacure™ EDB available fromLAMBERTI, H-Nu™ 470 and H-Nu™ 470X available from SPECTRA GROUP Ltd.

For safety reasons, the photoinitiator is preferably a so-calleddiffusion hindered photoinitiator. A diffusion hindered photoinitiatoris a photoinitiator which exhibits a much lower mobility in a curedlayer of the curable inkjet ink than a monofunctional photoinitiator,such as benzophenone. Several methods can be used to lower the mobilityof the photoinitiator. One way is to increase the molecular weight ofthe photoinitiator so that the diffusion speed is reduced, e.g.polymeric photoinitiators. Another way is to increase its reactivity sothat it is built into the polymerizing network, e.g. multifunctionalphotoinitiators (having 2, 3 or more photoinitiating groups) andpolymerizable photoinitiators. The diffusion hindered photoinitiator ispreferably selected from the group consisting of non-polymericmultifunctional photoinitiators, oligomeric or polymeric photoinitiatorsand polymerizable photoinitiators. Non-polymeric di- or multifunctionalphotoinitiators are considered to have a molecular weight between 300and 900 Dalton. Non-polymerizable monofunctional photoinitiators with amolecular weight in that range are not diffusion hinderedphotoinitiators. Most preferably the diffusion hindered photoinitiatoris a polymerizable initiator.

Suitable diffusion hindered photoinitiators are also those disclosed inEP 2053101 A (AGFA) in paragraphs [0074] and [0075] for difunctional andmultifunctional photoinitiators, in paragraphs [0077] to [0080] forpolymeric photoinitiators and in paragraphs [0081] to [0083] forpolymerizable photoinitiators.

Other preferred polymerizable photoinitiators are those disclosed in EP2065362 A (AGFA) and EP 2161264 A (AGFA), incorporated herein byreference.

A preferred amount of photoinitiator is 0-50 wt %, more preferably0.1-20 wt %, and most preferably 0.3-15 wt % of the total weight of thecurable inkjet ink.

Co-initiators

In order to increase the photosensitivity further, the radiation curableinkjet ink may additionally contain co-initiators. Suitable examples ofco-initiators can be categorized in three groups:

-   (1) tertiary aliphatic amines such as methyldiethanolamine,    dimethylethanolamine, triethanolamine, triethylamine and    N-methylmorpholine;-   (2) aromatic amines such as amylparadimethylaminobenzoate,    2-n-butoxyethyl-4-(dimethylamino) benzoate,    2-(dimethylamino)ethylbenzoate, ethyl-4-(dimethylamino)benzoate, and    2-ethylhexyl-4-(dimethylamino)benzoate; and-   (3) (meth)acrylated amines such as dialkylamino alkyl(meth)acrylates    (e.g., diethylaminoethylacrylate) or    N-morpholinoalkyl-(meth)acrylates (e.g.,    N-morpholinoethyl-acrylate).    The preferred co-initiators are aminobenzoates.

The one or more co-initiators included into the radiation curable inkjetink are preferably diffusion hindered co-initiators for safety reasons.A diffusion hindered co-initiator is preferably selected from the groupconsisting of non-polymeric di- or multifunctional co-initiators,oligomeric or polymeric co-initiators and polymerizable co-initiators.More preferably the diffusion hindered co-initiator is selected from thegroup consisting of polymeric co-initiators and polymerizableco-initiators.

The radiation curable inkjet ink preferably comprises a co-initiator inan amount of 0.1 to 50 wt %, more preferably in an amount of 0.5 to 25wt %, most preferably in an amount of 1 to 10 wt % of the total weightof the radiation curable inkjet ink.

Inhibitors

The radiation curable inkjet ink may further also contain at least oneinhibitor for improving the thermal stability of the ink.

Suitable polymerization inhibitors include phenol type antioxidants,hindered amine light stabilizers, phosphor type antioxidants,hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,and hydroquinone, t-butylcatechol, pyrogallol,2,6-di-tert.butyl-4-methylphenol (=BHT) may also be used.

Suitable commercial inhibitors are, for example, Sumilizer™ GA-80,Sumilizer™ GM and Sumilizer™ GS produced by Sumitomo Chemical Co. Ltd.;Genorad™ 16, Genorad™18 and Genorad™ 20 from Rahn AG; Irgastab™UV10 andIrgastab™ UV22, Tinuvin™ 460 and CGS20 from Ciba Specialty Chemicals;Floorstab™ UV range (UV-1, UV-2, UV-5 and UV-8) from Kromachem Ltd,Additol™ S range (S100, S110, S120 and S130) from Cytec SurfaceSpecialties.

The inhibitor is preferably a polymerizable inhibitor.

Since excessive addition of these polymerization inhibitors may lowerthe curing speed, it is preferred that the amount capable of preventingpolymerization is determined prior to blending. The amount of apolymerization inhibitor is preferably lower than 5 wt %, morepreferably lower than 3 wt % of the total radiation curable inkjet ink.

Colorants

Colorants used in the radiation curable inkjet inks may be dyes,pigments or a combination thereof. Organic and/or inorganic pigments maybe used. The colorant is preferably a pigment or a polymeric dye, mostpreferably a pigment.

The pigments may be black, white, cyan, magenta, yellow, red, orange,violet, blue, green, brown, mixtures thereof, and the like. A colourpigment may be chosen from those disclosed by HERBST, Willy, et al.Industrial Organic Pigments, Production, Properties, Applications. 3rdedition. Wiley—VCH, 2004. ISBN 3527305769.

Suitable pigments are disclosed in paragraphs [0128] to [0138] of WO2008/074548 (AGFA GRAPHICS).

Pigment particles in inkjet inks should be sufficiently small to permitfree flow of the ink through the inkjet-printing device, especially atthe ejecting nozzles. It is also desirable to use small particles formaximum colour strength and to slow down sedimentation.

The numeric average pigment particle size is preferably between 0.050and 1 μm, more preferably between 0.070 and 0.300 μm and particularlypreferably between 0.080 and 0.200 μm. Most preferably, the numericaverage pigment particle size is no larger than 0.150 μm. The averageparticle size of pigment particles is determined with a BrookhavenInstruments Particle Sizer BI90plus based upon the principle of dynamiclight scattering. The ink is diluted with ethyl acetate to a pigmentconcentration of 0.002 wt %. The measurement settings of the BI90plusare: 5 runs at 23° C., angle of 90°, wavelength of 635 nm andgraphics=correction function.

However for white pigment inkjet inks, the numeric average particlediameter of the white pigment is preferably from 50 to 500 nm, morepreferably from 150 to 400 nm, and most preferably from 200 to 350 nm.Sufficient hiding power cannot be obtained when the average diameter isless than 50 nm, and the storage ability and the jet-out suitability ofthe ink tend to be degraded when the average diameter exceeds 500 nm.The determination of the numeric average particle diameter is bestperformed by photon correlation spectroscopy at a wavelength of 633 nmwith a 4 mW HeNe laser on a diluted sample of the pigmented inkjet ink.A suitable particle size analyzer used was a Malvern™ nano-S availablefrom Goffin-Meyvis. A sample can, for example, be prepared by additionof one drop of ink to a cuvette containing 1.5 mL ethyl acetate andmixed until a homogenous sample was obtained. The measured particle sizeis the average value of 3 consecutive measurements consisting of 6 runsof 20 seconds.

Suitable white pigments are given by Table 2 in [0116] of WO 2008/074548(AGFA GRAPHICS). The white pigment is preferably a pigment with arefractive index greater than 1.60. The white pigments may be employedsingly or in combination. Preferably titanium dioxide is used as pigmentwith a refractive index greater than 1.60. Suitable titanium dioxidepigments are those disclosed in [0117] and in [0118] of WO 2008/074548(AGFA GRAPHICS).

The pigments are preferably present in the range of 0.01 to 15%, morepreferably in the range of 0.05 to 10% by weight and most preferably inthe range of 0.1 to 5% by weight, each based on the total weight of theinkjet ink. For white inkjet inks, the white pigment is preferablypresent in an amount of 3% to 40% by weight of the inkjet ink, and morepreferably 5% to 35%. An amount of less than 3% by weight cannot achievesufficient covering power and usually exhibits very poor storagestability and ejection property.

Generally dyes exhibit a higher light fading than pigments, but cause noproblems on jettability. It was found that anthraquinone dyes exhibitonly minor light fading under the normal UV curing conditions used in UVcurable inkjet printing. In a preferred embodiment, the colorant in theradiation curable inkjet ink is an anthraquinone dye, such as Macrolex™Blue 3R (CASRN 325781-98-4) from LANXESS.

Dispersants

The dispersant is preferably a polymeric dispersant. Typical polymericdispersants are copolymers of two monomers but may contain three, four,five or even more monomers. The properties of polymeric dispersantsdepend on both the nature of the monomers and their distribution in thepolymer. Suitable copolymeric dispersants have the following polymercompositions:

-   -   statistically polymerized monomers (e.g. monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g. monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g. monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g. monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with polymeric side chains attached to the backbone);        and mixed forms of these polymers, e.g. blocky gradient        copolymers.

Suitable polymeric dispersants are listed in the section on“Dispersants”, more specifically [0064] to [0070] and [0074] to [0077],in EP 1911814 A (AGFA GRAPHICS).

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30000, more preferably between 1500 and 10000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100000, more preferably smaller than 50000 andmost preferably smaller than 30000.

The polymeric dispersant has preferably a polydispersity PD smaller than2, more preferably smaller than 1.75 and most preferably smaller than1.5.

Commercial examples of polymeric dispersants are the following:

-   -   DISPERBYK™ dispersants available from BYK CHEMIE GMBH;    -   SOLSPERSE™ dispersants available from NOVEON;    -   TEGO™DISPERS™ dispersants from EVONIK;    -   EDAPLAN™ dispersants from MÜNZING CHEMIE;    -   ETHACRYL™dispersants from LYONDELL;    -   GANEX™ dispersants from ISP;    -   DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC        (BASF);    -   DISPONER™ dispersants from DEUCHEM; and    -   Joncryl™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include Solsperse™dispersants from NOVEON, Efka™ dispersants from CIBA SPECIALTY CHEMICALSINC (BASF) and Disperbyk™ dispersants from BYK CHEMIE GMBH. Particularlypreferred dispersants are Solspersen™ 32000, 35000 and 39000 dispersantsfrom NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt%, more preferably 5 to 200 wt % based on the weight of the pigment.

Dispersion Synergists

A dispersion synergist usually consists of an anionic part and acationic part. The anionic part of the dispersion synergist usuallyexhibits a certain molecular similarity with the colour pigment and thecationic part of the dispersion synergist consists of one or moreprotons and/or cations to compensate the charge of the anionic part ofthe dispersion synergist.

The synergist is preferably added in a smaller amount than the polymericdispersant(s). The ratio of polymeric dispersant/dispersion synergistdepends upon the pigment and should be determined experimentally.

Preferably the ratio wt % polymeric dispersant/wt % dispersion synergistis selected between 2:1 to 100:1, preferably between 2:1 and 20:1.

Suitable dispersion synergists that are commercially available includeSolsperse™ 5000 and Solsperse™ 22000 from NOVEON.

Suitable dispersion synergists include those disclosed in EP 1790698 A(AGFA GRAPHICS), EP 1790696 A (AGFA GRAPHICS), WO 2007/060255 (AGFAGRAPHICS) and EP 1790695 A (AGFA GRAPHICS)

In dispersing C.I. Pigment Blue 15:3, the use of a sulfonatedCu-phthalocyanine dispersion synergist, e.g. Solsperse™ 5000 from NOVEONis preferred. Suitable dispersion synergists for yellow inkjet inksinclude those disclosed in EP 1790697 A (AGFA GRAPHICS).

In a preferred embodiment, the dispersion synergist includes one, two ormore carboxylic acid groups and preferably no sulfonic acid groups.

Surfactants

The radiation curable inkjet ink may further also contain a surfactantfor obtaining good spreading characteristics on a substrate. Thesurfactant(s) can be anionic, cationic, non-ionic, or zwitterionic andare usually added in a total quantity less than 10 wt % based on thetotal weight of the radiation curable liquid or ink and particularly ina total less than 5 wt % based on the total weight of the radiationcurable liquid or ink.

Preferred surfactants include fluoro surfactants (such as fluorinatedhydrocarbons) and silicone surfactants. The silicones are typicallysiloxanes and can be polyether modified, polyester modified, polyethermodified hydroxy functional, amine modified, epoxy modified and othermodifications or combinations thereof. Silicone surfactants, especiallythe reactive silicone surfactants, are preferred in radiation curableinkjet inks.

In a preferred embodiment, the radiation curable inkjet ink contains nosurfactant.

Inkjet Printing Devices

In the inkjet printing method according to a preferred embodiment of thepresent invention, the radiation curable inkjet inks may be jetted byone or more print heads ejecting small droplets in a controlled mannerthrough nozzles onto a substrate, which is moving relative to the printhead(s).

A preferred print head for the inkjet printing system is a piezoelectrichead. Piezoelectric inkjet printing is based on the movement of apiezoelectric ceramic transducer when a voltage is applied thereto. Theapplication of a voltage changes the shape of the piezoelectric ceramictransducer in the print head creating a void, which is then filled withink. When the voltage is again removed, the ceramic expands to itsoriginal shape, ejecting a drop of ink from the print head. However theinkjet printing method according to preferred embodiments of the presentinvention is not restricted to piezoelectric inkjet printing. Otherinkjet print heads can be used and include various types, such as acontinuous type.

The inkjet print head normally scans back and forth in a transversaldirection across the moving ink-receiving metal surface. Often theinkjet print head does not print on the way back. Bi-directionalprinting is preferred for obtaining a high areal throughput. Anotherpreferred printing method is by a “single pass printing process”, whichcan be performed by using page wide inkjet print heads or multiplestaggered inkjet print heads which cover the entire width of theink-receiving metal surface. In a single pass printing process theinkjet print heads usually remain stationary and the metal surface istransported under the inkjet print heads.

Curing Devices

In the inkjet printing method according to a preferred embodiment of thepresent invention, the radiation curable inkjet inks are cured byexposing them to actinic radiation, preferably by ultraviolet radiation.

The curing device may be arranged in combination with the print head ofthe inkjet printer, travelling therewith so that the curable inkjet inkis exposed to curing radiation very shortly after been jetted.

In such an arrangement it can be difficult to provide a small enoughradiation source connected to and travelling with the print head, suchas LED. Alternatively, the actinic radiation may be supplied from afixed source to the radiation head by an arrangement of mirrorsincluding a mirror upon the radiation head.

The source of radiation arranged not to move with the print head, mayalso be an elongated radiation source extending transversely across theink-receiver surface to be cured and adjacent the transverse path of theprint head so that the subsequent rows of images formed by the printhead are passed, stepwise or continually, beneath that radiation source.

Any ultraviolet light source, as long as part of the emitted light canbe absorbed by the photo-initiator or photo-initiator system, may beemployed as a radiation source, such as, a high or low pressure mercurylamp, a cold cathode tube, a black light, an ultraviolet LED, anultraviolet laser, and a flash light. Of these, the preferred source isone exhibiting a relatively long wavelength UV-contribution having adominant wavelength of 300-400 nm. Specifically, a UV-A light source ispreferred due to the reduced light scattering therewith resulting inmore efficient interior curing.

UV radiation is generally classed as UV-A, UV-B, and UV-C as follows:

-   UV-A: 400 nm to 320 nm-   UV-B: 320 nm to 290 nm-   UV-C: 290 nm to 100 nm.

In a preferred embodiment of the method of inkjet printing according tothe present invention, the inkjet printing device contains one or moreUV LEDs with a wavelength larger than 360 nm, preferably one or more UVLEDs with a wavelength larger than 380 nm, and most preferably UV LEDswith a wavelength of about 395 nm.

Furthermore, it is possible to cure the image using, consecutively orsimultaneously, two light sources of differing wavelength orilluminance. For example, the first UV-source can be selected to be richin UV-C, in particular in the range of 260 nm-200 nm. The secondUV-source can then be rich in UV-A, e.g. a gallium-doped lamp, or adifferent lamp high in both UV-A and UV-B. The use of two UV-sources hasbeen found to have advantages e.g. a fast curing speed and a high curingdegree.

For facilitating curing, the inkjet printer may include one or moreoxygen depletion units. The oxygen depletion units place a blanket ofnitrogen or other relatively inert gas (e.g. CO₂), with adjustableposition and adjustable inert gas concentration, in order to reduce theoxygen concentration in the curing environment. Residual oxygen levelsare usually maintained as low as 200 ppm, but are generally in the rangeof 200 ppm to 1200 ppm.

EXAMPLES Materials

All materials used in the following examples were readily available fromstandard sources such as ALDRICH CHEMICAL Co. (Belgium) and ACROS(Belgium) unless otherwise specified. The water used was deionizedwater.

ITX is Darocur™ ITX is an isomeric mixture of 2- and4-isopropylthioxanthone from CIBA SPECIALTY CHEMICALS.

Irgacure™ 907 is2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, aphotoinitiator available from CIBA SPECIALTY CHEMICALS.

Irgacure™ 819 is bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, aphotoinitiator available from CIBA SPECIALTY CHEMICALS.

Darocur™TPO is 2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide, aphotoinitiator available from CIBA SPECIALTY CHEMICALS.

MBF is an aromatic photoinitiator (CAS 15206-55-0) available asSpeedcure™ MBF from LAMBSON.

Inhib-1 is a mixture forming a polymerization inhibitor having acomposition:

Component wt % DPGDA 82.4 p-methoxyphenol 4.0 2,6-di-tert-butyl-4- 10.0methylphenol Cupferron ™ AL 3.6

Cupferron™ AL is aluminum N-nitrosophenylhydroxylamine from WAKOCHEMICALS LTD.

-   Macrolex™ Blue 3R is a blue anthraquinone dye from LANXESS.

Isola™ 400 is a Cu-plate available from CCI Eurolam having a metalsurface consisting of a 18μ Cu-laminate.

The monomers are listed here below with their abbreviation as used inthe Examples.

-   -   Sartomer grades are available from SARTOMER.    -   Miramer grades are available from MIWON Europe GmbH.    -   Laromer grades are available from BASF.    -   VEEA is available from NIPPON SHOKUBAI, Japan.    -   Cardura™ ACE is available from HEXION SPECIALTY CHEMICALS.    -   ACMO is available from RAHN AG.    -   MAES is available from ALDRICH.    -   MADAME is available from ARKEMA France.

Monomer Commercial name Chemical name ACE Cardura ™ ACE Glycerinet.decanoate acrylate DCPA Laromer ™ DCPA Dicyclopentadienyl acrylateTBCH Laromer ™ TBCH 4-t.Butylcyclohexyl acrylate M140 Miramer ™ M1402-Phenoxyethyl acrylate M202 Miramer ™ M202 1,6-Hexanediol (3xethoxylated) diacrylate M280 Miramer ™ M280 Polyethylene glycol (MW400)diacrylate M282 Miramer ™ M282 Polyethylene glycol (MW200) diacrylateM286 Miramer ™ M286 Polyethylene glycol (MW600) diacrylate M3130Miramer ™ M3130 Trimethylolpropane (3x ethoxylated) triacrylate CD420Sartomer ™ CD420 3,3,5-Trimethylcyclohexyl acrylate CD561 Sartomer ™CD561 1,6-Hexanediol (5.6x ethoxylated) diacrylate CD9021 Sartomer ™Glycerine (5.5x propoxylated) CD9021 triacrylate SR205 Sartomer ™ SR205Triethylene glycol dimethacrylate SR206 Sartomer ™ SR206 Ethylene glycoldimethacrylate SR209 Sartomer ™ SR209 Tetraethylene glycoldimethacrylate SR210 Sartomer ™ SR210 Polyethylene glycol (MW200)dimethacrylate SR213 Sartomer ™ SR213 1,4-Butanediol diacrylate SR230Sartomer ™ SR230 Diethylene glycol diacrylate SR238 Sartomer ™ SR2381,6-Hexanediol diacrylate SR239 Sartomer ™ SR239 1,6-Hexanedioldimethacrylate SR252 Sartomer ™ SR252 Polyethylene glycol (MW600)dimethacrylate SR259 Sartomer ™ SR259 Polyethylene glycol (MW200)diacrylate SR272 Sartomer ™ SR272 Triethylene glycol diacrylate SR339Sartomer ™ SR339 2-Phenoxyethyl acrylate SR344 Sartomer ™ SR344Polyethylene glycol (MW400) diacrylate SR350 Sartomer ™ SR350Trimethylolpropane trimethacrylate SR351 Sartomer ™ SR351Trimethylolpropane triacrylate SR454 Sartomer ™ SR454 Trimethylolpropane(3x ethoxylated) triacrylate SR492 Sartomer ™ SR492 Trimethylolpropane(3x propoxylated) triacrylate SR499 Sartomer ™ SR499 Trimethylolpropane(6x ethoxylated) triacrylate SR506D Sartomer ™ Isobornyl acrylate SR506DSR508 Sartomer ™ SR508 Dipropylene glycol diacrylate SR610 Sartomer ™SR610 Polyethylene glycol (MW600) diacrylate SR9003 Sartomer ™Neopentylglycol (2x SR9003 propoxylated) diacrylate SR9020HP Sartomer ™Glycerine (3x propoxylated) SR9020HP triacrylate SR9035 Sartomer ™Trimethylolpropane (15x SR9035 ethoxylated) triacrylate SR9054Sartomer ™ 2-hydroxyethyl methacrylate SR9054 phosphate MAES noneMono-2-(methacryloyloxy)ethyl succinate ACMO none N-Acryloyl morpholineMADAME Norsocryl ™ N,N-dimethyl 2-aminoethyl MADAME methacrylate VEEAnone 2-(2′-Vinyloxyethoxy)ethyl acrylate

Measurements 1. Etch Resistance

The etch resistance was evaluated by the determining the percentage ofthe cured inkjet ink layer that remained on the copper plate afteretching. An etch resistance of 100% means that the whole cured inkjetink layer survived the etching bath. An etch resistance of 0% means thatno cured inkjet ink could be found to be present on the copper plateafter etching. An intermediate percentage, e.g. 80% means that about 80%of the cured inkjet ink could be found to be present on the copper plateafter etching. A good etch resistance means a value of at least 80%.Excellent etch resistance means a value of at least 90% but preferably100%.

2. Strippability

The strippability was evaluated by the determining the percentage of thecured inkjet ink layer that was removed from the copper plate afterstripping. A strippability of 100% means that the whole cured inkjet inklayer was removed. A strippability of 0% means that no cured inkjet inkcould be removed from the copper plate. An intermediate percentage, e.g.30% means that only about 30% of the cured inkjet ink could be removedfrom the copper plate by stripping. A good strippability means a valueof at least 80%. Excellent strippability means a value of at least 90%but preferably 100%. A value of 30% or less is a very poorstrippability.

3. Viscosity

The viscosity of the formulations was measured at 45° C. using a“Robotic Viscometer Type VISCObot” from CAMBRIDGE APPLIED SYSTEMS.

For industrial inkjet printing, the viscosity is preferably less than 20mPa·s at 45° C. More preferably the viscosity is less than 15 mPa·s at45° C.

4. Curing Speed

A radiation curable inkjet ink was coated on a PET100 substrate using abar coater and a 10 μm wired bar. The coated sample was cured using aFusion DRSE-120 conveyer, equipped with a Fusion VPS/1600 lamp (D-bulb),which transported the samples under the UV-lamp on a conveyer belt at aspeed of 20 m/min. The maximum output of the lamp was 1.05 J/cm² and apeak intensity of 5.6 W/cm². The percentage of the maximum output of thelamp was taken as a measure for curing speed, the lower the number thehigher the curing speed. A sample was considered as fully cured at themoment scratching with a Q-tip caused no visual damage.

Example 1

This example illustrates an inkjet printing method for an etchingprocess using a radiation curable inkjet ink including a singlepolymerizable compound.

Preparation of the Radiation Curable Inkjet Inks

The radiation curable inkjet inks COMP-1 to COMP-18 and INV-1 to INV-24were prepared by mixing the components according to the weightpercentages based on the total weight of the ink listed in Table 1 andusing the polymerizable compound of Table 2.

TABLE 1 Component wt % ITX 5.00 Irgacure ™ 907 5.00 Irgacure ™ 819 3.00Darocur ™ TPO 2.00 Inhib-1 1.00 Macrolex ™ Blue 3R 1.75 Polymerizable82.25 compound

Isola™ 400 copper plates were cleaned for 5 seconds at 25° C. with asolution called Mecbrite™ CA-95 from MEC Europe, which has pH<1 andcontained H₂SO₄, H₂O₂ and Cu²⁺. During this operation a thin top layerof Cu (0.3-0.5 μm) was removed. The plates were then rinsed with a waterjet for 90 seconds.

A pattern of the radiation curable inkjet inks COMP-1 to COMP-18 andINV-1 to INV-24 was coated at a thickness of 10 pm on the copper plateand cured by a Fusion DRSE-120 conveyer, equipped with a Fusion VPS/I600lamp (D-bulb), which transported the samples under the UV-lamp on aconveyer belt at a speed of 20 m/min. The maximum output of the lamp was1.05 J/cm² and a peak intensity of 5.6 W/cm². All inkjet inks were fullycured.

The plates were subjected to an acidic etch bath (“Mega” acid etchantobtained from Mega Electronics, pH 2, contains FeCl₃) for 60 seconds at35° C. The plates were subsequently rinsed for 90 seconds with water anddried. An evaluation of the etch resistance was then made as shown inTable 2.

The copper plates having their inkjet ink layer removed during etchingcould naturally not be evaluated for strippability (in Table 2 markedwith nab.). The other copper plates were subjected for 5 minutes at 50°C. to an alkaline strip bath (containing 10% Ristoff C-71 from CenturionSpeciality Chemicals Ltd which includes 7% ethanolamine, pH 13),thenrinsed for 90 seconds with water, dried, and evaluated forstrippability. The results are shown in Table 2.

TABLE 2 Inkjet Polymerizable Etch ink compound OFR WPF ResistanceStrippability COMP-1 CD420 0.163 0.0051 100%  0% COMP-2 M284 0.3690.0049  0% n.a. COMP-3 DCPA 0.157 0.0049 100%  0% COMP-4 ACE 0.2660.0033 100%  0% COMP-5 TBCH 0.152 0.0048 100%  0% COMP-6 SR506D 0.1540.0048 100%  0% COMP-7 SR339 0.250 0.0052 100%  0% COMP-8 M140 0.2500.0052 100%  0% COMP-9 MADAME 0.204 0.0064  0% n.a. COMP-10 SR495 0.3250.0029  0% n.a. COMP-11 ACMO 0.227 0.0071  0% n.a. COMP-12 SR252 0.3520.0027  0% n.a. COMP-13 CD561 0.325 0.0042  0% n.a. COMP-14 SR9035 0.3510.0031  0% n.a. COMP-15 SR610 0.366 0.0028  0% n.a. COMP-16 M286 0.3660.0028  0% n.a. COMP-17 M280 0.368 0.0039  0% n.a. COMP-18 SR344 0.3680.0039  0% n.a. INV-1 VEEA 0.344 0.0054 100% 100% INV-2 SR499 0.3420.0054 100% 100% INV-3 SR259 0.370 0.0065 100% 100% INV-4 M282 0.3700.0065 100% 100% INV-5 M202 0.312 0.0056 100% 100% INV-6 SR210 0.3390.0059 100% 100% INV-7 SR209 0.339 0.0061 100% 100% INV-8 SR205 0.3350.0070 100% 100% INV-9 SR272 0.372 0.0077 100% 100% INV-10 CD9021 0.3210.0052 100% 100% INV-11 SR350 0.284 0.0089 100% 100% INV-12 SR508 0.3300.0083 100% 100% INV-13 SR9003 0.292 0.0061 100% 100% INV-14 SR213 0.3230.0101 100% 100% INV-15 SR351 0.324 0.0101 100% 100% INV-16 M220 0.3200.0067 100% 100% INV-17 SR230 0.373 0.0093 100% 100% INV-18 SR239 0.2520.0079 100% 100% INV-19 SR9020HP 0.336 0.0070 100% 100% INV-20 SR2060.323 0.0101 100% 100% INV-21 SR492 0.306 0.0064 100% 100% INV-22 SR2380.283 0.0088 100% 100% INV-23 SR454 0.336 0.0070 100% 100% INV-24 M31300.336 0.0070 100% 100%

Evaluation

From Table 2, it should be clear that only the radiation curable inkjetinks wherein the polymerizable composition has an oxygen fractionOFR>0.250 and a weighted polymerizable functionality WPF≧0.0050 resultedin excellent etch resistance and strippability.

Example 2

This example illustrates an inkjet printing method for an etchingprocess using a radiation curable inkjet ink including a mixture of twopolymerizable compounds.

Preparation of the Radiation Curable Inkjet Inks

The radiation curable inkjet inks COMP-19 to COMP-30 and INV-25 toINV-54 were prepared by mixing the components according to Table 3 andusing the polymerizable compounds P1 and P2 in the weight percentagesbased on the total weight of ink as indicated in Table 4.

TABLE 3 Component wt % ITX 5.00 Irgacure ™ 907 5.00 Irgacure ™ 819 3.00Darocure ™ TPO 2.00 Inhib-1 1.00 Macrolex ™ Blue 3R 1.75 Polymerizabletogether compound P1 82.25 Polymerizable compound P2

Isola™ 400 copper plates were cleaned in the same manner as inEXAMPLE 1. A pattern of the radiation curable inkjet inks COMP-19 toCOMP-30 and INV-25 to INV-54 was coated at a thickness of 10 μm andcured on the cleaned copper plate in the same manner as in EXAMPLE 1.The plates were then etched and stripped in the same manner as inEXAMPLE 1. The results are shown in Table 4.

TABLE 4 Etch Inkjet Mixture wt % wt % Resis- Strip- Ink P1/P2 P1 P2 OFRWPF tance pability COMP-19 SR508/ 2.25 80.00 0.325 0.0043  0% n.a. CD561COMP-20 SR238/ 2.25 80.00 0.324 0.0043  60% 100% CD561 COMP-21 SR610/2.25 80.00 0.326 0.0042  0% n.a. CD561 COMP-22 SR610/ 22.25 60.00 0.3360.0038  0% n.a. CD561 COMP-23 SR610/ 42.25 40.00 0.346 0.0035  0% n.a.CD561 COMP-24 SR610/ 62.25 20.00 0.356 0.0032  0% n.a. CD561 COMP-25SR610/ 10.00 72.25 0.179 0.0046 100%  10% SR506D COMP-26 SR610/ 20.0062.25 0.205 0.0043 100%  20% SR506D COMP-27 SR610/ 50.00 32.25 0.2830.0036  30% 100% SR506D COMP-28 SR610/ 70.00 12.25 0.335 0.0031  0% n.a.SR506D COMP-29 SR610/ 60.00 22.25 0.344 0.0045  0% n.a. SR238 COMP-30SR610/ 70.00 12.25 0.354 0.0037  0% n.a. SR238 INV-25 SR508/ 12.25 70.000.326 0.0048  95% 100% CD561 INV-26 SR508/ 22.25 60.00 0.326 0.0053 100%100% CD561 INV-27 SR508/ 32.25 50.00 0.327 0.0058 100% 100% CD561 INV-28SR508/ 42.25 40.00 0.328 0.0063 100% 100% CD561 INV-29 SR508/ 52.2530.00 0.328 0.0068 100% 100% CD561 INV-30 SR508/ 62.25 20.00 0.3290.0073 100% 100% CD561 INV-31 SR508/ 72.25 10.00 0.330 0.0078 100%  90%CD561 INV-32 SR238/ 12.25 70.00 0.319 0.0049  95% 100% CD561 INV-33SR238/ 22.25 60.00 0.313 0.0055 100% 100% CD561 INV-34 SR238/ 32.2550.00 0.308 0.0060 100% 100% CD561 INV-35 SR238/ 42.25 40.00 0.3030.0066 100% 100% CD561 INV-36 SR238/ 52.25 30.00 0.298 0.0072 100% 100%CD561 INV-37 SR238/ 62.25 20.00 0.293 0.0077 100%  90% CD561 INV-38SR238/ 72.25 10.00 0.288 0.0083 100%  90% CD561 INV-39 SR259/ 10.0072.25 0.293 0.0086 100% 100% SR238 INV-40 SR259/ 20.00 62.25 0.3040.0083 100% 100% SR238 INV-41 SR259/ 30.00 52.25 0.315 0.0080 100%  80%SR238 INV-42 SR259/ 40.00 42.25 0.325 0.0077 100% 100% SR238 INV-43SR259/ 50.00 32.25 0.336 0.0074 100% 100% SR238 INV-44 SR259/ 52.2530.00 0.338 0.0073 100% 100% SR238 INV-45 SR259/ 52.25 30.00 0.3380.0073 100% 100% SR238 INV-46 SR259/ 60.00 22.25 0.347 0.0071 100% 100%SR238 INV-47 SR259/ 70.00 12.25 0.357 0.0068 100% 100% SR238 INV-48SR259/ 40.00 42.25 0.259 0.0056 100% 100% SR506D INV-49 SR259/ 50.0032.25 0.285 0.0058 100% 100% SR506D INV-50 SR259/ 60.00 22.25 0.3120.0060 100% 100% SR506D INV-51 SR259/ 70.00 12.25 0.338 0.0062 100% 100%SR506D INV-52 SR610/ 10.00 72.25 0.293 0.0081 100% 100% SR238 INV-53SR610/ 20.00 62.25 0.303 0.0074 100% 100% SR238 INV-54 SR610/ 30.0052.25 0.313 0.0066 100% 100% SR238

Evaluation

From Table 4, it should be clear that only the radiation curable inkjetinks wherein the polymerizable composition has an oxygen fractionOFR>0.250 and a weighted polymerizable functionality WPF≧0.0050 resultedin good to excellent etch resistance and strippability.

Example 3

This example illustrates the applicability of radiation curable inkjetinks to a wide range of etch process conditions.

Preparation of the Radiation Curable Inkjet Inks

The radiation curable inkjet inks COMP-31 to COMP-42 and INV-55 toINV-77 were prepared by mixing the components according to Table 5 andusing the polymerizable compounds P1 (and P2 if present) in the weightpercentages based on the total weight of ink as indicated in Table 6.

TABLE 5 Component wt % ITX 5.00 Irgacure ™ 907 5.00 Irgacure ™ 819 3.00Darocure ™ TPO 2.00 Inhib-1 1.00 Macrolex ™ Blue 3R 1.75 Polymerizabletogether compound P1 82.25 Polymerizable compound P2 (if present)

TABLE 6 Polymerizable Inkjet compound(s) P1 wt % of wt % of Ink (/P2) P1P2 OFR WPF COMP-31 ACE 82.25 0.00 0.266 0.0033 COMP-32 CD420 82.25 0.000.163 0.0051 COMP-33 DCPA 82.25 0.00 0.157 0.0049 COMP-34 TBCH 82.250.00 0.152 0.0048 COMP-35 SR506D 82.25 0.00 0.154 0.0048 COMP-36 SR506D82.25 0.00 0.154 0.0048 COMP-37 SR610 82.25 0.00 0.366 0.0028 COMP-38SR610/SR506D 10.00 72.25 0.179 0.0046 COMP-39 SR610/SR506D 20.00 62.250.205 0.0043 COMP-40 SR610/SR506D 50.00 32.25 0.283 0.0036 COMP-41SR610/SR238 60.00 22.25 0.344 0.0045 COMP-42 SR610/SR238 70.00 12.250.354 0.0037 INV-55 CD9021 82.25 0.00 0.321 0.0052 INV-56 M220 82.250.00 0.320 0.0067 INV-57 SR205 82.25 0.00 0.335 0.0070 INV-58 SR20682.25 0.00 0.323 0.0101 INV-59 SR209 82.25 0.00 0.339 0.0061 INV-60SR210 82.25 0.00 0.339 0.0059 INV-61 SR213 82.25 0.00 0.323 0.0101INV-62 SR230 82.25 0.00 0.373 0.0093 INV-63 SR238 82.25 0.00 0.2830.0088 INV-64 SR238 82.25 0.00 0.283 0.0088 INV-65 SR238 82.25 0.000.283 0.0088 INV-66 SR239 82.25 0.00 0.252 0.0079 INV-67 SR259/SR23852.25 30.00 0.338 0.0073 INV-68 SR259/SR506D 50.00 32.25 0.285 0.0058INV-69 SR272 82.25 0.00 0.372 0.0077 INV-70 SR350 82.25 0.00 0.2840.0089 INV-71 SR351 82.25 0.00 0.324 0.0101 INV-72 SR492 82.25 0.000.306 0.0064 INV-73 SR499 82.25 0.00 0.342 0.0054 INV-74 SR508 82.250.00 0.330 0.0083 INV-75 SR9003 82.25 0.00 0.292 0.0061 INV-76 SR9020HP82.25 0.00 0.336 0.0070 INV-77 VEEA 82.25 0.00 0.344 0.0054

Isola™ 400 copper plates were cleaned in the same manner as inEXAMPLE 1. A pattern of the radiation curable inkjet inks COMP-31 toCOMP-42 and INV-55 to INV-77 was coated at a thickness of 10 μm andcured on the cleaned copper plate in the same manner as in EXAMPLE 1.

A first set of these copper plates was then etched and stripped in thesame manner as in EXAMPLE 1, the results thereof indicated in Table 7 byEtch Resistance “Acid” respectively Strippability “Acid”.

A second set of copper plates made with the radiation curable inkjetinks COMP-31 to COMP-42 and INV-55 to INV-77 was subjected for 60seconds at 35° C. to an alkaline etch bath Metal etch 50 from CenturionSpeciality Chemicals Ltd which contained NH₄OH, NH₄Cl, (NH₄)₂CO₃ andCu(NH₄)Cl₃ at pH 8.5. The plates were subsequently rinsed for 90 secondswith water and dried. The copper plates having their inkjet ink layernot removed during etching were subjected for 5 minutes at 50° C. to analkaline strip bath (containing 10% Ristoff C-71 from CenturionSpeciality Chemicals Ltd which includes 7% ethanolamine, pH 13),thenrinsed for 90 seconds with water, dried, and evaluated forstrippability. The results of etching and stripping are indicated inTable 7 by Etch Resistance “Alkaline” respectively Strippability“Alkaline”.

A third set of copper plates made with the radiation curable inkjet inksCOMP-31 to COMP-42 and INV-55 to INV-77 was etched in the same manner asin EXAMPLE 1. A TESAFILM 4014 Black tape (type PV-025-066-B4104 5) fromTesa AG was attached to the pattern of the radiation curable inkjet inkon the copperplate. The tape was then pulled from the copper plate,thereby peeling off the pattern in a number of cases. The strippabilityresults are indicated Table 7 by Strippability “Dry Strip”.

TABLE 7 Strippability Inkjet Etch Resistance Dry Ink Acid Alkaline AcidAlkaline Strip COMP-31 100% 100%  0%  0%  0% COMP-32 100% 100%  0%  0% 0% COMP-33 100% 100%  0%  0%  0% COMP-34 100% 100%  0%  0%  0% COMP-35100% 100%  0%  0%  0% COMP-36 100% 100%  0%  0%  0% COMP-37  0%  0% n.a.n.a. n.a. COMP-38 100% 100%  10%  0%  0% COMP-39 100%  90%  20%  20%  0%COMP-40  30%  0% 100% n.a. 100% COMP-41  0%  0% n.a. n.a. n.a. COMP-42 0%  0% n.a. n.a. n.a. INV-55 100% 100% 100% 100% 100% INV-56 100% 100%100% 100% 100% INV-57 100% 100% 100% 100% 100% INV-58 100% 100% 100%100% 100% INV-59 100%  80% 100% 100% 100% INV-60 100%  80% 100% 100%100% INV-61 100%  90% 100% 100% 100% INV-62 100%  90% 100% 100% 100%INV-63 100%  80%  80% 100% 100% INV-64 100%  90% 100%  90% 100% INV-65100%  90% 100% 100% 100% INV-66 100% 100% 100% 100% 100% INV-67 100% 90% 100% 100% 100% INV-68 100%  85% 100% 100% 100% INV-69 100%  90%100% 100% 100% INV-70 100% 100% 100% 100% 100% INV-71 100% 100% 100%100% 100% INV-72 100% 100% 100% 100% 100% INV-73 100%  95% 100% 100%100% INV-74 100%  95% 100% 100% 100% INV-75 100% 100% 100% 100% 100%INV-76 100% 100% 100% 100% 100% INV-77 100%  90% 100% 100% 100%

Table 7 shows that only the radiation curable inkjet inks wherein thepolymerizable composition has an oxygen fraction OFR>0.250 and aweighted polymerizable functionality WPF≧0.0050 supported very differentetching and stripping conditions.

Example 4

In Examples 1 to 3, the radiation curable inkjet inks INV-1 to INV-77provided good to excellent etch resistance and strippability.

The radiation curable inkjet inks COMP-1, COMP-3 to COMP-8, COMP-25,COMP-26, COMP-31 to COMP-36, COMP-37 and COMP-8 exhibited good toexcellent etch resistance but no strippability. These inks including apolymerizable composition having an oxygen fraction OFR≦0.250 and aweighted polymerizable functionality WPF≦0.0055, exhibited good etchresistance but no strippability. Although these inks are useless as etchresistant ink for creating a conductive pattern of a printed circuitboard, they can be used as a so-callled “legend ink”. By printing thelegend inkjet ink and the etch resistant inkjet ink simultaneously on acopper plate, with the legend inkjet ink being printed in a position notcovering the conductive pattern or copper circuitry, a simpler andcost-effective manufacturing process of printed circuit boards can berealized.

Example 5

This example illustrates the negative effect of acid monomers on thestability and curing speed of radiation curable inkjet inks for makingetch resists.

Preparation of the Radiation Curable Inkjet Inks

The radiation curable inkjet inks COMP-43 to COMP-58 and INV-78 toINV-81 were prepared by mixing the components according to Tables 8 to11. The weight percentages on the total weight of the inkjet ink.

TABLE 8 wt % of Component: COMP- COMP- COMP- INV-78 INV79 43 44 45 ITX5.00 5.0  5.00 5.00 5.00 Irgacure ™ 907 5.00 — 5.00 — 5.00 Irgacure ™819 3.00 3.00 3.00 3.00 3.00 MBF — 5.00 — 5.00 — Darocure ™ TPO 2.002.00 2.00 2.00 2.00 Inhib-1 1.00 1.00 1.00 1.00 1.00 Macrolex ™ Blue 3R1.75 1.75 1.75 1.75 1.75 SR350 82.25  82.25  72.25 72.25 77.25 SR9054 —— 10.00 10.00 5.00 MAES — — — — —

TABLE 9 wt % of Component: COMP- COMP- COMP- COMP- COMP- 46 47 48 49 50ITX 5.00 5.00 5.00 5.00 5.00 Irgacure ™ 907 — 5.00 — 5.00 — Irgacure ™819 3.00 3.00 3.00 3.00 3.00 MBF 5.00 — 5.00 — 5.00 Darocure ™ TPO 2.002.00 2.00 2.00 2.00 Inhib-1 1.00 1.00 1.00 1.00 1.00 Macrolex ™ Blue 3R1.75 1.75 1.75 1.75 1.75 SR350 77.25  72.25  72.25  62.25  62.25  SR90545.00 — — — — MAES — 10.00  10.00  20.00  20.00 

TABLE 10 wt % of Component: INV- INV- COMP- COMP- COMP- 80 81 51 52 53ITX 5.00 5.00 5.00 5.00 5.00 Irgacure ™ 907 5.00 — 5.00 — 5.00Irgacure ™ 819 3.00 3.00 3.00 3.00 3.00 MBF — 5.00 — 5.00 — Darocure ™TPO 2.00 2.00 2.00 2.00 2.00 Inhib-1 1.00 1.00 1.00 1.00 1.00 Macrolex ™Blue 3R 1.75 1.75 1.75 1.75 1.75 SR238 30.00 30.00 25.00 25.00 27.25SR259 52.25 52.25 47.25 47.25 50.00 SR9054 — — 10.00 10.00 5.00 MAES — —— — —

TABLE 11 wt % of Component: COMP- COMP- COMP- COMP- COMP- 54 55 56 57 58ITX 5.00 5.00 5.00 5.00 5.00 Irgacure ™ 907 — 5.00 — 5.00 — Irgacure ™819 3.00 3.00 3.00 3.00 3.00 MBF 5.00 — 5.00 — 5.00 Darocure ™ TPO 2.002.00 2.00 2.00 2.00 Inhib-1 1.00 1.00 1.00 1.00 1.00 Macrolex ™ Blue 3R1.75 1.75 1.75 1.75 1.75 SR238 27.25 25.00 25.00 20.00 20.00 SR259 50.0047.25 47.25 42.25 42.25 SR9054 5.00 — — — — MAES — 10.00 10.00 20.0020.00

Evaluation

All the radiation curable inkjet inks COMP-43 to COMP-58 and INV-78 toINV-81 had a polymerizable composition having an oxygen fractionOFR>0.250 and a weighted polymerizable functionality WPF≧0.0050. Nohomogeneous inkjet ink could be prepared for the compositions accordingto COMP-43 and COMP-45, some components could not be dissolvedadequately and therefore no further tests were performed on these inks.All the radiation curable inkjet inks contained no surfactant, yet allhad a surface tension between 20 and 40 mN/m measured with a KRÜSStensiometer K9 from KRÜSS GmbH, Germany at 25° C. after 60 seconds.

The viscosity of inkjet inks was measured directly after preparation andagain after a heat treatment of 1 week at 80° C. If an increase inviscosity of 10% or more was observed than the ink received the score“Yes”, if no increase or an increase less than 10% was observed than theink received the score “No. The results are shown in Table 12.

As the curing speed depends highly on the photoinitiators and monomersthe radiation curable inkjet inks COMP-43 to COMP-58 were compared withthe most comparable reference inkjet inks: INV-78 (Ref.1), INV-79(Ref.2, INV-80 (Ref.3) and INV-81 (Ref.4). The results for curing speedare shown in Table 12.

Isola™ 400 copper plates were cleaned in the same manner as inEXAMPLE 1. A pattern of the radiation curable inkjet inks COMP-43 toCOMP-58 and INV-78 to INV-81 was coated at a thickness of 10 μm andcured on the cleaned copper plate in the same manner as in EXAMPLE 1.The plates were then etched and stripped in the same manner as inEXAMPLE 1. Excellent etch resistance was observed for all inkjet inks.The results of strippability are shown in Table 12.

TABLE 12 Viscosity Inkjet Initial 1 week Curing speed Strip- Ink OFR WFR(mPa · s) at 80° C. Versus Loss? pability INV-78 0.284 0.0089 19.5 NoRef. 1 n.a. 100% INV-79 0.284 0.0089 16.1 No Ref. 2 n.a. 100% COMP-430.298 0.0086 Inhomogeneous Inkjet ink COMP-44 0.298 0.0086 25.4 Yes Ref.2 No  40% COMP-45 0.291 0.0087 Inhomogeneous Inkjet ink COMP-46 0.2910.0087 21.7 Yes Ref. 2 No  0% COMP-47 0.300 0.0083 22.4 Solid Ref. 1 No 10% COMP-48 0.300 0.0083 20.2 Solid Ref. 2 No  20% COMP-49 0.316 0.007825.6 Solid Ref. 1 No  40% COMP-50 0.316 0.0078 20.7 Solid Ref. 2 No  60%INV-80 0.338 0.0074 8.7 No Ref. 3 n.a. 100% INV-81 0.338 0.0074 8.3 NoRef. 4 n.a. 100% COMP-51 0.346 0.0072 16.0 Yes Ref. 3 Yes 100% COMP-520.346 0.0072 10.7 Yes Ref. 4 Yes 100% COMP-53 0.342 0.0073 12.2 Yes Ref.3 Yes 100% COMP-54 0.342 0.0073 9.0 Yes Ref. 4 Yes 100% COMP-55 0.3490.0069 10.9 Yes Ref. 3 No 100% COMP-56 0.349 0.0069 10.0 No Ref. 4 Yes100% COMP-57 0.360 0.0065 13.9 No Ref. 3 Yes 100% COMP-58 0.360 0.006511.9 No Ref. 4 Yes 100%

From Table 12, it should be clear that inkjet printing with highstability at high curing speed was only possible with radiation curableinkjet inks INV-78 to INV-81 which had a polymerizable compositionhaving an oxygen fraction OFR>0.250 and a weighted polymerizablefunctionality WPF≧0.0050 and a polymerizable composition containing nopolymerizable compound with an ethylenic double bond and including aphosphoester group or a carboxylic acid group in the molecule thereof.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. (canceled)
 2. A radiation curable inkjet ink for etch resistcomprising: at least 70 percent by weight of a polymerizable compositionbased on a total weight of the radiation curable inkjet ink; wherein thepolymerizable composition has an oxygen fraction OFR>0.250 and aweighted polymerizable functionality WPF≧0.0050;${OFR} = {{\sum\limits_{i = 1}^{n}{\frac{15.9994 \times N_{O,i} \times \% \mspace{14mu} {wt}_{i}}{{MW}_{i} \times \% \mspace{14mu} {wt}_{P}}{\mspace{31mu} \mspace{14mu}}{WPF}}} = {\sum\limits_{i = 1}^{n}\frac{N_{P,i} \times \% \mspace{14mu} {wt}_{i}}{{MW}_{i} \times \% \mspace{14mu} {wt}_{P}}}}$n=a number of polymerizable compounds in the polymerizable compositionhaving a different chemical structural formula from each other;N_(O,i)=a number of oxygen atoms in polymerizable compound i;N_(P,i)=anumber of polymerizable groups in the polymerizable compound i; MW_(i)=amolecular weight of the polymerizable compound i; % wt_(i)=a weightpercentage of the polymerizable compound i based on the total weight ofthe radiation curable inkjet ink; % wt_(P)=a weight percentage of thepolymerizable composition based on the total weight of the radiationcurable inkjet ink; and the polymerizable composition contains nopolymerizable compound with an ethylenic double bond including aphosphoester group and contains no polymerizable compound with anethylenic double bond and a carboxylic acid group.
 3. The radiationcurable inkjet ink for etch resist according to claim 2, wherein thepolymerizable composition contains at least one polymerizable compoundselected from the group consisting of 1,6-hexanediol diacrylate,1,4-butanediol diacrylate, 2-(2′-vinyloxyethoxy)ethyl acrylate,triethyleneglycol diacrylate, triethyleneglycol dimethacrylate,propoxylated neopentylglycol diacrylate, propoxylated glycerinetriacrylate, trimethylolpropane trimethylacrylate, tripropylene glycoldiacrylate, diethylene glycol diacrylate, dipropylene glycol diacrylate,ethoxylated trimethylolpropane triacrylate, and propoxylatedtrimethylolpropane triacrylate.
 4. The radiation curable inkjet ink foretch resist according to claim 2, wherein the n polymerizable compoundsall have a viscosity of less than 40 mPa·s at 25° C.
 5. An etched metalor alloy printed with a polymerized radiation curable inkjet ink foretch resist according to claim
 2. 6. The etched metal or alloy accordingto claim 5, wherein the etched metal or alloy contains copper.
 7. Theetched metal or alloy according to claim 5, further comprising aradiation curable inkjet legend ink, wherein the radiation curableinkjet legend ink includes a polymerizable composition having an oxygenfraction OFR≦0.250 and a weighted polymerizable functionalityWPF≦0.0055.